How can I implement async dependencies with knockout-postbox?

[fbuchinger]

I want to implement ajax-powered dependencies between knockout.observables (e.g. country -> province -> city selection) using postbox. When the user selects a country, an ajax request to a dependencyController should be issued, which in turn responds with values for the dependent province and cities fields.

How can I update the observable values in the publishOn/subscribeTo callbacks?

Here is my initial implementation:

 var CountryDependency = function() {
        var self = this;
        this.country = ko.observable("Austria").publishOn("country");
        this.province = ko.observable().subscribeTo("country", function(newValue){
            $.get('/dependencyController?country=' + self.country(), function(response){
               //how can i update province with the value from the server?
                newValue = response.province;
            });
        }).publishOn("province");
        this.cities = ko.observable().subscribeTo("province", function (newValue){
            //another ajax request to dependency controller here
        });
    };

[rniemeyer]

Hello- Here is a sample that uses manual subscriptions to update dependent dropdowns via AJAX requests: http://jsfiddle.net/rniemeyer/nj3ps/. Maybe you can take a look at that sample first and then we can discuss if you do need to involve postbox in the equation or not. Thanks!

[fbuchinger]

Hi Ryan,

thanks for the helpful example! Turns out I don't need postbox for the ajax updates.